This application claims the priority of German Patent Document 102 36 380.3, filed Aug. 8, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a recuperative exhaust-gas heat exchanger for a gas turbine engine, said recuperative exhaust-gas heat exchanger having a crossflow/counterflow matrix around which hot turbine exhaust gas flows, a distributing tube for directing air delivered by a compressor into the crossflow/counterflow matrix, and a collecting tube which is arranged parallel to the distributing tube and is intended for discharging the compressor air, heated via the crossflow/counterflow matrix, to a consumer, end faces of the distributing and collecting tubes which are remote from the compressor and consumer being closed.
The use of recuperative exhaust-gas heat exchangers in gas turbine engines is known. Such exhaust-gas heat exchangers, in addition to a heat exchanger casing, basically comprise a distributing tube for feeding “cold” air, delivered by a compressor, into a “crossflow/counterflow matrix”, around which the hot turbine exhaust gas flows, and a collecting tube for discharging the now heated “hot” compressor air to a suitable consumer, e.g. the combustion chamber of the gas turbine engine. Those end faces of the distributing and collecting tubes which are remote from the compressor and consumer are as a rule of closed design. The feeding of the air from the distributing tube into the crossflow/counterflow matrix or the discharge of the air from the crossflow/counterflow matrix into the collecting tube is effected via a plurality of openings/holes arranged one behind the other and made in the lateral surface of the tubes. In order to be able to achieve the desired rate of flow, a plurality of such hole rows have to be provided in the axial direction. Those regions of the lateral surface of the distributing and collecting tubes which have the holes are referred to below as a hole zone.
The crossflow/counterflow matrix comprises in turn a multiplicity of hairpin-shaped lancets or tubes combined to form a tube bundle. Each tube within the tube bundle corresponds with an associated opening from the hole zone of the distributing and collecting tubes. Each tube bundle is in each case fastened to the distributing tube and the collecting tube arranged parallel thereto and is arranged such as to project laterally in a U shape. German Patent Document DE-C 36 35 548 and corresponding U.S. Pat. No. 4,800,955, for example, have disclosed such a heat exchanger.
Furthermore, German Patent Document DE 41 18 777 A1 and corresponding U.S. Pat. No. 5,243,815 disclose a device for the compact connection of a recuperative exhaust-gas heat exchanger to a gas turbine engine. The design in this case is such that loads acting on the heat exchanger, such as force due to weight, shock loads, e.g. as the cause of non-steady operating states, or the like, are not absorbed by the heat exchanger casing itself, but are passed via “intermediate plates” directly into the gas turbine casing. A design feature of the disclosed device consists, inter alia, in the fact that the collecting tube is mounted in an axially movable manner in the region of its closed end face.
In this case, as experience has shown, the fact that the force which acts on the closed end face of the collecting tube due to the high internal pressure is not passed directly into the turbine casing proves to be disadvantageous. On the contrary, these forces are passed via the lateral surface of the collecting tube to the opposite end face of the collecting tube. In the hole zone, which has a high notch factor as a result of the hole rows in the axial tube axis direction, this force flow leads to high stress peaks and thus to increased wear and short service life.
An aspect of the invention is to resolve these problems by a novel design of the mounting of such distributing and collecting tubes which avoids the disadvantages.
Starting from a recuperative exhaust-gas heat exchanger of the type mentioned at the beginning, this aspect may be achieved according to certain preferred embodiments of the invention in that the closed end face of the collecting tube is firmly connected axially and radially to the turbine casing.
In this amazingly simple manner, it is now ensured that the forces acting on the closed end face of the collecting tube can be passed directly into the turbine casing, that is to say a force flow from the closed end face of the collecting tube directly into the turbine casing is ensured.
The mounting of the collecting tube according to certain preferred embodiments of the invention leads to substantial advantages.
By the specific guiding of the force flow directly into the turbine casing, the stress peaks in the notch radii are markedly reduced. This leads to a marked prolongation of the service life of the component, a factor which at the same time results in cost savings. The constructional components required may also be designed to be lighter than hitherto.
According to an embodiment of the invention, the region comprising the closed end face of the collecting tube is designed as a cover plate. The cover plate is preferably releasably connected to the collecting tube. The use of a releasable cover plate proves to be advantageous, since the cover plate can be attached to both end faces of the collecting tube and thus use or repair is facilitated.
An exchanger casing which is free of load and thus optimized in terms of weight is ensured by the collecting tube likewise being mounted in the turbine casing in the region of its open end face facing the consumer.
In order to ensure stress-free mounting of the collecting tube, that mounting of the collecting tube which is assigned to the open end face is designed with axial bearing play.
According to a further embodiment of the invention, the end faces of the collecting tube have respective tube bends for the air feed and the air discharge, and the collecting tube is mounted in the turbine casing in the region of the two tube bends. In this case, the collecting tube is firmly mounted axially and radially in the region of the one tube bend, whereas in the region of the other tube bend the mounting of the collecting tube is designed with axial bearing play. The axial forces of the tube bends are passed directly into the casing and do not load the collecting tube. This design also has the advantages mentioned at the beginning.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.